Testing of a high-speed digital data transmission system for drill pipe in a 4500 ft well at the Rocky Mountain Oilfield Testing Center in Casper, Wyoming is described. Passive transmission of digital data through a series of four segments of telemetry drill pipe of approximately 1000 ft each has been successfully achieved. Data rates of 2 Mbit/sec have been tested through the 4500 ft system with very low occurrence of data errors.